# What the differences between BDM1 spaces and \[P1,P1\] spaces?

**URL:** <https://community.freefem.org/t/what-the-differences-between-bdm1-spaces-and-p1-p1-spaces/607>\
**Category:** General Discussion\
**Created:** [October 9, 2020, 3:21am UTC](https://community.freefem.org/t/what-the-differences-between-bdm1-spaces-and-p1-p1-spaces/607 "2020-10-09T03:21:04Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![SunFan](https://avatars.discourse-cdn.com/v4/letter/s/b487fb/32.png) [@SunFan](https://community.freefem.org/u/SunFan)\
**Post date:** [October 9, 2020, 3:21am UTC](https://community.freefem.org/t/what-the-differences-between-bdm1-spaces-and-p1-p1-spaces/607/1 "2020-10-09T03:21:04Z")

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For 3d simulations, we want to use BDDF spaces, but FreeFem++ do not have this type of spaces, only have RT03d. So we can see the definition of BDM1 or BDDF1 spaces is that the vector belongs to P1^2, so why we can not use [P1, P1] spaces to substitute? Or is there any open sources about how to construct the BDM1 spaces in FreeFem++?